CA1216878A

CA1216878A - Colour display tube

Info

Publication number: CA1216878A
Application number: CA000460259A
Authority: CA
Inventors: Hans G. Gerlach
Original assignee: Individual
Current assignee: Koninklijke Philips NV
Priority date: 1983-08-05
Filing date: 1984-08-02
Publication date: 1987-01-20
Also published as: PL249062A1; DD223566A5; EP0134059A3; KR920001870B1; NL8302773A; DE3474881D1; ES534821A0; JPH053695B2; EP0134059B1; US4626738A; EP0134059A2; KR850002161A; SG52090G; ES8505142A1; JPS6054143A

Abstract

ABSTRACT:
.
"Colour display tube"

A colour display tube comprising in an evacuated envelope (1) which is composed of a neck (4), a cone (3) and a display window (2), in said neck a system of electron guns (5) with which three electron beams are generated which are situated with their axes in one plane and which are focused by means of a focusing lens field on a display screen (10) provided on the inside of the display window, which focusing lens field is formed between two electrodes (25, 26) of the electron gun system which are situated behind each other along the axes, which electrodes comprise facing outermost edges (32, 33) and three apertures (38, 39, 40, 42, 43, 44) which are symmetrical with respect to the said plane and through which the electron beams pass within these edges in a recessed part (34, 41) extending substantially at right angles to the axes. By making in such a display tube the shape of the central aperture (39, 43) in at least one of the electrodes so that this, in addition to providing a quadrupole component, substan-tially compensates an eight-pole component in the focusing lens field at the area of the central electron beam and making the shape of the outermost apertures in at least one of the electrodes so that this, in addition to providing a quadrupole component, substantially compensates a six-pole component in the focusing lens field at the area of the outermost electron beams, a better spot on the display screen is obtained.

Description

7~1 PHN 10.752 1 20.10.83 "Colour Display Tube".

The invention relates to a colour display tu~e ccmprising in an evacuated envelope which is composed of a neck, a cone and a display window, in said neck a system of electron guns with which three electron ~eams situated with their axes in one plane are generated, which keams are focused, by means of a focusing lens field, on a display screen which is provided on the inside of the display window, which focusing lens field is formed ketween two electrodes of the system of electron guns situated one kehind the other along the axes, which electrodes comprise outermost edges facing each other and within these edges three apertures through which the electron keams pass are provided symmetrically with respect to the said plane in a recessed part exterdin~ substantially at right angles to the axes.
Such a colour display tube is known frcm United States Patent Specification 4,370,592. It is also stated in the said Patent Specification that the focusing lens field generated in this manner still is astigmatic and the electron keams are focused vertically more strongly than horizontally. As described in said Patent Specification, said astigmatism is corrected by providing the second electrode of the focusing lens with a plate having an elongate slot which is provided on the side of the display screen. Said slot is situated symmetrically with respect to the plane through the beam axes. Hcwever, it has been found that said corrections of the horizontal/vertical asti~matism are not sufficient since the quality of the spot on the display screen nevertheless leaves something to ke desired.
The United Kingdom Patent Application 2.112.564 descrikes also such a colour display tube. The horizontal/vertical asti~matism is eliminated by making the apertures in the recessed part elongate.
m is is also not sufficient to get smaller spot dimensions.
It is therefore an object of the invention to provide measures to improve the quality of the spot ~nd to obtain smaller dimensions of the spot than with the known tukes with comparable keam currents.
For that purpose, according to the invention, a colour display 87~
PHN 10.752 2 20.10.83 tuke of the kind described in the opening paragraph is characterized in that the shape of the central aperture in at least one of the electrodes is such that this, in addition to providing a quadrupole component, substantially compensates for an eight-pole co~ponent in the focusing lens field at the area of the central electron beam, and the shape of the outermost apertures in at least one of the electrodes is such that this, in addition to providing a quadrupole component, substantially compensates for a six-pole component in the focusing lens field at the area of the outermost electron keams.
o m e invention is based on the recognition obtained experimentally and from computations that, because the three electron keams are situated with their axes in one plane and within facing outerm~st edges, not only a different focusing in a horizontal and a vertical direction t~kes place, but also in directions situated inketween. Around the central keam is formed in particular an eight-pole component and around the outer keams is formed in particular a six-pole component in the focusing lens field. m ese multipole ccm~onents must ke compensated for at least for the greater part. According to the invention this can ke done by giving the apertures in the electrodes ketween which the focusing lens field is generated such a shape deviating from a circular aperture that in addition to the quadrupole component for the central beam, a compensating eight-pole component is obtained and for the outermost keams a compensating six-pole component is obtained. The horizonta V vertical astigmatism can ke compensated for substantially ky the quadrupole component in the lens field. However it is also possible to allow a quantity of horizontal/vertical astigmatism to be present in the focusing lens field which then compensates for the astigmatism of the deflection coils.
It has also been found that there is an optimum distan oe by which the outermost edge projects akove the recessed part. Therefore, a first preferred embodiment of a colour display tuke in accordance with the invention is characterized in that the outermost edge projects above the recessed part by a distance which is equal to 10 to 25% of the largest diameter of the recessed portion within the outermost edge.
When the distance is sm~ller, the influence of the shape of the apertures on the lens field predominates and reduces the effective lens diameter. When the distance is larger, the influence of the apertures is too small to ke able to readily correct the akerra-~21~B~8 PHN 10.752 3 20.10.83 tions. The electrodes usually have an oval cross-section at right angles to the longitudinal axis of the system of electron guns.
Hcwever, it is also possible for the electrodes to have a circular orthogonal cross-section. A compensating eight-pole component in the focusing lens field can ke generated bymaking the central aperture in the recessed portion of the first and/or the second electrode substantially octagonal as well as elongate to obtain a quadrupole component. A compensating six-pole component in the focusing lens field can be generated by making the outermost apertures substantially pear-shaped. A second preferred embodiment of the colour display tube inaccordance with the invention is therefore characterized in that, viewed in the direction of propagation of the electron keams, the central aperture in at least the first electrode of the two electrodes between which the focusing lens field is formed is elongate, the long axis keing at right angles to the said plane, the edge of said aperture forming substantially an octagon, the outermost apertures being pear-shaped and the edges of the said apertures, viewed from the central aperture, converging outwards. A focusing lens formed between two electrodes may be considered to be composed of tw~ lens parts, a positive lens part (equipotential lines convex in the direction of the electrode of low potential) and a weaker negative lens part (equipotential lines co~vex in the direction of the electrode of high potential). The strength of the positive lens part is always greater than that of the negative lens part, so that the two lens parts together have a positive lens action.
If the apertures in the second electrode of the focusing lens have the same shape as the apertures in the first electrode, the influence of the apertures in the first electrode on the positive lens part is attenuated by the influence of the apertures in the second electrode on the negative lens part. mlS will ke entered into herein-after.
A third preferred em~cdiment of the colour display tube in accordance with the invention is characterized in that, viewed in the direction of propagation of the electron keams, the central aperture in the second electrode of the two electrodes ketween which the focusing lens field is formed is elongate, the long axis of said aperture being situated in the said plane, the ed~e of the said aperture substantially form m g an octagon, the outerm3st apertures keing substan-871~
PHN 10.752 4 20.10.83 tially pear-shaped, the edges of the said apertures, viewed from the central aperture, diverging outwards.
By constructing the apertures in the second electrode in this manner, the desired correction can also ke obtained. The desired correction can also be achieved by ccmbination of the first and the second preEerred emkcdiments. It will ke obvious that the desired eight-pole and six-pole components can also ke obtained by providing, for example, an elongate, substantially octagonal central aperture in the first electrode with the long axis of the aperture at right angles to the said plane and two outwardly diverging, substantially pear-shaped, outermost apertures in the second electrode of the focusing lens.
It is also possible to obtain the desired eight-pole and six-pole components, for example, by providing an elongate, substantially octagonal central aperture having its long axis in the said plane in lS the second electrode and two outwardly converging, substantially pear-shaped outermost apertures in the first electrode. However, from a technical point of view of production this is less attractive.
The pear-shaped apertures are obtained in a simple manner by composing them, viewed from the central aperture, of outwardly or inwardly converging isosceles trapeziums which are closed by arcs of circles on the outside and/or inside.
m e invention will now be descri~ed in greater detail, by way of example, with reference to the accompanying drawing, in which:
Figure 1 is a longitudinal sectional view of a colour display tube according to the invention, Figure 2 is a longitudinal sectional view of an electron gun system as used in the colour display tuke of Figure 1, Figure 3 is an elevation of a lens electrcde of Figure 2, Figure 4 shows the diameter of the spot on the display screen as a function of the keam current for three colour display tu~es, Figure 5 is another elevation of a lens electrode of Figure

2, and Figure 6 shows an alternative pear-shaped aperture.
Figure 1 is a longitudinal sectional view of a colour display 35 tube of the so-called "in-line" type. An integrated electron gun system 5 is provided in a glass envelope 1 which is composed of a display window 2, a cone 3, and said neck 4; the electron gun system generates three electron beams 6,7 and 8 which are situated with their .~ .

-- iZ16~37~
PHN 10.752 5 20.10.83 axes in the plane of the drawing. The axis of the central electron beam 7 initially coincides with the tube axis 9. On its inside the display window 2 comprises a large num~er of triplets of phosphor lines.
Each triplet co~,prises a line consisting of a blue-luminescing phosphor, a line consisting of a green-luminescing phosphor and a line consisting of a red-luminescing phosphor. All triplets together constitute the display screen 10. The phosphor lines are at right angles to the plane of the drawing. In front of the display screen is positioned the shadow mask 11 in which a large numker of elongate apertures 12 are provided through which the electron beams 6, 7 and 8 pass, which beams each impinge onLy on phosphor lines of one colour. The three electron keam~s which are situated in one plane are deflected by the system of deflection coils 13.
Figure 2 is a longitudinal sectional view of the electron gun system as used in the colour display tuke shown in Figure 1. The electron gun system comprises a ccmmon cup-shaped control electrode 20 in which three cathodes 21, 22 and 23 are connected, and a common plate-shaped anode 24. The three electron keams situated with their axes in one plane are focused by means of the electrodes 25 and 26 which are common for the three electron beams. Electrode 25 consists of two cup-shap~d parts 27 and 28 which are connected together with their open ends. Electrode 26 comprises one cup-shaped part 29 and a centring sleeve 30 the kottom of which has apertures 31 through which the electron keams pass. Electrode 25 has an outer edge 32 extending towards electrode 26 and electrode 26 has an outer edge 33 extending towards electrode 25. Apertures 38, 39 and 40 are provided in the recessed part 34 which extends at right angles to the axes 35, 36 and 37 of the electron keams 6, 7 and 8. Apertures 42, 43 and 44 are provided in the re oe ssed part 41 which extends substantially at right angles to the axis 36 of the oe ntral electron beam. m e recessed parts 34 and 41 can form one assembly with the parts 28 and 29, respectively, just like in the electron gun which is disclosed in United States Patent Specification 4,370,592. The apertures in the re oe ssed parts may also comprise coIlars. Because the edg 33 comprises a larger aperture than edge 32, the electron keams converge after the focusing lens.
However, it is also possible to let the electron beams converge already in or after the triode part of the electron gun which is formed by the cathcde snd the elsctr~des 20, 24 and 25. See for example, Unlted S ates ~2~

PHN. 10.752 6 :Patent Specification 4,291,251. The.wall of the electrodes 25 and 26 is, for example, 0.25 mm thick. The slot between the electrodes 25 and 26 is, for example, 1 ~m wide. The distance between the axes of the electron b~ams'35,'.36 and'36,'37 is, for example, 4.45 mm.
Figure 3 is an elevation of lens electrode 25 of Figure 2.
By making the aperture' 39 to be sub'stantially octagonal and elongate, the long axis being at right angles to the plane through the beam axes 35,':36 and 37, the line of intersection 45 of which with the plane of the.drawing being shcw.n, the eight-pole camponent which is formed in the focusing lens field by the edges'32 and''33 is substantially com-pensated for, in addition to the horizontal/vertical astigmatism. The corners of the octagon may:be rounded off with which also higher-order multipoles are ccmpensated for. It is also possible to construct the sides :46 and 47 which.are now.parts of a circle, to be straight. By 15 making the apertures'38 an~ 40 to be substantially pear-shaped, the edge of the apertures,. viewed.from the central aperture'39, converging outwardly, the:six pcle component which is formed in the focusing lens field by the edges'32 and'33, is substantially compensated for.
Such pear-shaped and octag~nal apertures:can:easily be 20. reali~ed by starting fron a circle.~broken lines), parts (48,49) of the:circle being replaced by their chords (50,51).
A pear.shaped aperture realized in this ~nner:has:an edge :having the shape of an isosceles.trapezium, the:base and the top line . being replaced by.arcs of a circle. A:part of the.arc 52 may be 25. replaced'by its chord 53 (show~ in.broken lines).
The:outermost.broke~-line circles:have a:radius of, for example 2.15 mm and the central circle:has:a:radius'of 1.9 ~m. The . beam.axes'35 and'.36 and the bea~ a~es':36 and 37.are, for example, 4~.45 ~m apart. In`a system of axes X-Y with the point of intersection 30 . in the plane of the:.drawing:having axis":36 as centre, the:corner points A, B, C and ~ are situated in'the:locations indicated in the :table~
~ ~ Y(~n) ' l A 0.8 1.72 B 1.:56 0.65 C '3.:96 2.09 D 5.. 46 1.90 -~2~8~

PHN. 10.752 7 The edge 32 exten~s 2 mm above the recessed part 34. The apertures'38 and 40.are identical and symmetrical with respect to the X-axis. Aperture'39 is situated symmetrically with respect to the X-axis and the Y-axis.
Figure 4 shows the spot diameter d (in mm) on the display screen as a function of the electron beam current I (in mA) for the central electron beam of three electron guns. Line A is the.variation of the spot diameter as a function of the beam current in an electron gun of the conventional type without an edge and recessed:part. Line B is the:variation of the spot diameter as a function of the becam current in an electron gun according to United States Patent Specifica-tion 4,370,592. Line C denotes the v.ariation of the spot diameter as : a function of the beam current in an electron gun for a colour display tube according to the invention. The electrodes 25 and 26.are con-structed in acoordance wLth Figures 2 and 3. From this camparison itfollows that, by using the:invention, the spot diameter is smaller : both at high and at low beam currents,. as a result of which a sharper picture:can be displayed. In tubes according to the invention a 10 to 20% smaller spot was established than in tubes in which the inven-tion.was not used. By using apertures as shown in Figure 3 in elec-.trode 25r the desired eight-pole and six-pole component corrections .can be obtained in addition to the four-pole co~ponent correction.
By m~king the apertures shown to be more or less elongate, the four-pole aomponent in the focusing lens field at the.æ ea of the beams:can 25: also be co~pensated as desired or be adjusted at a given value. By using the:same shape for the aperture as in Figure 3 in electrode 26, the six-pole correction and the eight-pole oorrection are attenuated.
The use of identical lens components, however,:has advantages to which will be referred hereinafter.
Figure 5 shows another emkodiment of the lens electrode 26 of Figure 2. Aperturè 43, as aperture 39 in Figure 3, is sub'stantially octagonal and elonga-te. m e long axis of the~:said aperture, howev.er, now lies in the plane through the electron beam axes of which the line of intersection 54 with the plane of -the.drawing is shown. `By such a .
shape of the aperture, the eight-pole ocmponent which is formed in the:focusing lens field by the:edges'32 and 33 is substantially com-pensated in addition to the four-pole component. The.apertures 42 lZ1~37~

PEN. 10.752 and 44 are substantially pear-shaped. The edge of -the apertures diverges outwards, hc~ev.er. The six-pole component which is formed in the focusing lens field by the edges 32 and 33 is compensated substan-tially by the said apertures. m e different location of the apertures in electrode 26 as compared with the location in electrode 25 is the result of the fact that:the focusing lens may be considered to bP com-posed of a positive lens.part followed by a weaker negative lens part.
By reducing the diameter of the aperture in a given direction in electrode 25, the lens kecomes stronger in that direction because the positive lens part is situated near electrode 25. By reducing the diameter of the aperture in electrode 26 in a given direction, the lens becomes weaker in that direction, kecause the negative lens :part is situated near electrode 26. .From this it follows that the diameters of -the apertures in the:electrodes 25 and 26 must be:v æ ied oppositely to each other to.produce the:same effect.
However, if the aperture in the electrodes 25 and 26 have the~:same shape, a correction nevertheless:takes place because the positive lens part is always stronger than the negative lens:part. The choice of the same shape of the:apertures in the electrodes 25 and 26 may be attractive for technical reasons in the:production. As des-.cribed in European:Patent Application EP 103,923 published March 28, 1984, the astigmatism of the electron beams:can also still be reduced by m~king the lens electrode ccmponents between which the:lens field is ormed in an operating electron gun to be identical . The:lens electrode com~onents should ke.provided so that the corresponding sides.are:facing each other and the:corresponding apertures are opposite to:each other. By providing identical oomponents for the lens electrodes opposite to each other in the:~nner described it is : achieved that the deviations.from the desired shape of the oppositely located apertures, which deviations:have.arisen during the.manufacture of the apertures,.are approw~nately equally:large. As a result of this the:disturbing influence on the electron beams for the tw~ lens elec-.trodes is also app.roximately equally:large, but:of opposite sign, as . a result of which the astigmatism:resulting.from:said deuiations 35: becQmes-smaller.
m e pear-shaped apertures may:also be constructed as is shown in Figure 6. The straight lines 60,. 61,. 62,: 63 and 64 aga.in.are ~, .Zl ,~
, .. ...

1%1~B7~i~
PHN 10.752 9 20.10.83 chords of a circle of which the arcs 65, 66 and 67 are stil1 left.
It is also possible to obtain the four-, six- and eight-pole components in the focusing lens field by makiny the apertures in the recessed parts circular and providing them with collars of whic h the height, proceeding along the circumference, varies in height (corrugated collars). Hcwever, these collars are difficult to manufacture by means of polygonal drawing dies, for example a hexagonal or octayonal drawing die in a plate having round apertures. It is also possible to use a circuL~r drawing die in a plate having hexagonal or octagonal apertures. The collars may also be mdde oblique so as to produce convergence.

~5 ' .
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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PRO-PERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A colour display tube comprising in an evacuated envelope which is composed of a neck, a cone and a display window, in said neck a system of electron guns with which three electron beams situated with their axes in one plane are generated, which beams are focused, by means of a focusing lens field, on a display screen which is provided on the inside of the display window, which focusing lens field is formed between two electrodes of the system of electron guns situated one behind the other along the axes, which electrodes comprise outermost edges facing each other and within these edges three apertures through which the electron beams pass are provided symmetrically with respect to the said plane in a recessed part extending substantially at right angles to the axes, characterized in that the shape of the central aperture in at least one of the electrodes is such that this shape, in addition to providing a quadrupole component, substantially compensates for an eight-pole com-ponent in the focusing lens field at the area of the central electron beam, and the shape of the outermost aperture in at least one of the electrodes is such that this shape, in addition to providing a quadrupole component, substantially compensates for a six-pole component in the focusing lens field at the area of the outermost electron beams.

2. A colour display tube as claimed in Claim 1, char-acterized in that the outermost edge projects over the recessed part by a distance which is equal to 10 to 25% of the largest diameter of the recessed part within the outermost edge.

3. A colour display tube as claimed in Claim 1, char-acterized in that, viewed in the direction of propagation of the electron beams, the central aperture in at least the first electrode of the two electrodes between which the focus-ing lens field is formed, is elongate, the long axis being at right angles to the said plane, the edge of the said aperture forming substantially an octagon, the outermost apertures being pear-shaped and the edges of the said apertures, viewed from the central aperture, converging outwardly.

4. A colour display tube as claimed in Claim 2, char-acterized in that, viewed in the direction of propagation of the electron beams, the central aperture in at least the first electrode of the two electrodes between which the focusing lens field is formed, is elongate, the long axis being at right angles to the said plane, the edge of the said aperture forming substantially an octagon, the outer-most being pear-shaped and the edges of the said apertures, viewed from the central aperture, converging outwardly.

5. A colour display tube as claimed in Claim 1, char-acterized in that, viewed in the direction of propagation of the electron beams, the central aperture in the second elec-trode of the two electrodes between which the focusing lens field is formed, is elongate, the long axis of the said aperture being situated in the said plane, the edge of the said aperture forming substantially an octagon and the outer-most apertures being substantially pear-shaped, the edges of the said apertures, viewed from the central aperture, diverg-ing outwardly.

6. A colour display tube as claimed in Claim 2, char-acterized in that, viewed in the direction of propagation of the electron beams, the central aperture in the second elec-trode of the two electrodes between which the focusing lens field is formed, is elongate, the long axis of the said aperture being situated in the said plane, the edge of the said aperture forming substantially an octagon and the outermost apertures being substantially pear-shaped, the edges of the said apertures, viewed from the central aperture, diverging outwardly.

7. A colour display tube as claimed in Claim 3, char-acterized in that, viewed in the direction of propagation of the electron beams, the central aperture in the second elec-trode of the two electrodes between which the focusing lens field is formed, is elongate, the long axis of the said aperture being situated in the said plane, the edge of the said aperture forming substantially an octagon and the outermost apertures being substantially pear-shaped, the edges of the said apertures, viewed from the central aperture, diverging outwardly.

8. A colour display tube as claimed in Claim 4, char-acterized in that, viewed in the direction of propagation of the electron beams, the central aperture in the second elec-trode of the two electrodes between which the focusing lens field is formed, is elongate, the long axis of the said aperture being situated in the said plane, the edge of the said aperture forming substantially an octagon and the outermost apertures being substantially pear-shaped, the edges of the said apertures, viewed from the central aper-ture, diverging outwardly.

9. A colour display tube as claimed in Claim 3, 4 or 5, characterized in that the pear-shaped apertures are formed by isosceles trapeziums converging outwardly or in-wardly viewed from the central aperture and being closed on the inside and/or the outside by arcs of a circle.

10. A colour display tube as claimed in Claim 6, 7 or 8, characterized in that the pear-shaped apertures are formed by isosceles trapeziums converging outwardly or in-wardly viewed from the central aperture and being closed on the inside and/or the outside by arcs of a circle.